1. Field of the Invention
The present invention relates to an oxygen concentration sensor, and more particularly to an oxygen concentration sensor with an electrical connection suited for the transmission of different operating voltages.
2. Description of Background Information
Feedback control of the air/fuel ratio is generally utilized for controlling an internal combustion engine for the purification of exhaust gas and improvements of the fuel economy. For such a feedback control, oxygen concentration in exhaust gas is detected and the air/fuel ratio of mixture to be supplied to the engine is controlled in response to a result of detection.
Recently, a type of oxygen concentration sensor has been developed which can generate an output signal whose level is proportional to the oxygen concentration in exhaust gas. With such an oxygen concentration sensor, air/fuel ratio of the mixture to be taken into the engine is controlled very minutely.
For example, Japanese Patent Application Laid Open No. 58-153155 discloses an oxygen concentration sensor disposed in the exhaust gas of an internal combustion engine, which comprises an oxygen pump element (referred to simply as "pump element" hereinafter) an oxygen concentration detection cell element (referred to as "cell element" hereinafter), both made of an oxygen-ion conductive solid electrolyte member and a heater element for heating up the pump element and the cell element in proportion to an electric power current supplied thereto. By this measure, the pump element and the cell element are activated and the oxygen concentration in the exhaust gas is electrically sensed by means of these elements (also referred to as sensor elements) cooperating with each other. This type of oxygen concentration sensor is connected to a control unit for a feedback control of the air/fuel ratio of intake mixture on the basis of an output signal of the oxygen concentration sensor, and for maintaining a desirable operating condition of the oxygen concentration sensor.
FIGS. 1-3 show an example of the oxygen concentration sensor which is to be connected to a control unit for a sensing operation. As shown, the connection is performed by means of a single connector 1 having a plurality of terminals therein. More particularly, the oxygen concentration sensor shown in these figures includes a pump element 2', a cell element 3' and a heater element 4'. The connector 1 includes terminals 2a' and 2b' for the pump element 2', terminals 3a' and 3b' for the cell element 3', and terminals 4a' and 4b' for a heater element 4' which are arranged parallel to each other.
Through the terminals 3a' and 3b', a relatively low operating voltage of, for example 0 through 80 mV, from the cell element 3' is transmitted. On the other hand, through the terminals 2a' and 2b', 4a' and 4b', relatively high operating voltages of the pump element 2' and the heater element 4', for example 0 through 14 V, are transmitted. Therefore, in the event that water permeates into the inside of connector 1, leakage of the relatively high voltage of the pump element 2' and the heater element 4' into the terminals 3a' and 3b' may occur. If such a leakage occurs, it may result in an abnormal state of the output signal of the oxygen concentration sensor or damage to electric circuits in the control unit.